Abstract Concrete filled steel tubular columns are gaining its popularity in engineering practice. However, local buckling is the main criteria which effects on strength and ductility for the composite columns. In order to enhance their overall performance, one of the most effective measures is to provide stiffeners for the steel tubes. In the present research, experimental studies have been devoted to investigating the behavior of self-compacting Concrete Filled Steel Tube (CFST) stub columns strengthened by single or double stiffeners. A total of 36 stub columns specimen under monotonic compression load were tested in order to discover the best configuration of column system where (specimen having zero stiffeners, single stiffener, double stiffeners) each for hollow steel and with SCC in-filled are tested for 7 days, 28 days and 56 days strength with circular cross-sections of dimensions 300mm height x100mm diameter x 2mm thickness. The experimental results indicated that the use of Stiffeners strengthen the CFST has a significant effect on the overall behavior of CFST such as enhancement on its strength and ductility. Also the Stiffeners confinement delays local buckling of steel tube, prevents a sudden strength reduction caused by the local buckling of the steel tube, and increases lateral confinement of the concrete core. It is found that the best configuration of Stiffeners in the Steel tubes is providing it in transverse direction with single and double stiffeners at a height of h/2 and h/3 respectively.

1. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 05 Issue: 08 | Aug-2016, Available @ http://ijret.esatjournals.org 68
EXPERIMENTAL INVESTIGATION ON TRIPLE BLENDED SCC
FILLED STEEL TUBES WITH AND WITHOUT STIFFENERS
Naveen Kumar Y R1, Sharada S A2, G Narayana3
1
Master of Technology (Structural Engineering) Student, Civil Department, S J C Institute of Technology,
Chickballapur, Karnataka, India,
2
Assistant Professor, Civil Department, S J C Institute of Technology, Chickballapur, Karnataka, India,
3
Professor & Head of Civil Engineering Department, S J C Institute of Technology,Chickballapur, Karnataka, India.
Abstract
Concrete filled steel tubular columns are gaining its popularity in engineering practice. However, local buckling is the main
criteria which effects on strength and ductility for the composite columns. In order to enhance their overall performance, one of
the most effective measures is to provide stiffeners for the steel tubes. In the present research, experimental studies have been
devoted to investigating the behavior of self-compacting Concrete Filled Steel Tube (CFST) stub columns strengthened by single
or double stiffeners. A total of 36 stub columns specimen under monotonic compression load were tested in order to discover t he
best configuration of column system where (specimen having zero stiffeners, single stiffener, double stiffeners) each for hollow
steel and with SCC in-filled are tested for 7 days, 28 days and 56 days strength with circular cross-sections of dimensions 300mm
height x100mm diameter x 2mm thickness. The experimental results indicated that the use of Stiffeners strengthen the CFST has a
significant effect on the overall behavior of CFST such as enhancement on its strength and ductility. Also the Stiffeners
confinement delays local buckling of steel tube, prevents a sudden strength reduction caused by the local buckling of the steel
tube, and increases lateral confinement of the concrete core. It is found that the best configuration of Stiffeners in the St eel tubes
is providing it in transverse direction with single and double stiffeners at a height of h/2 and h/3 respectively.
Keywords: Composite Columns, Concrete Filled Steel Tube, Stiffeners, Self Compact Concrete etc.,
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1. INTRODUCTION
Concrete Filled Steel Tubes (CFST) is a composite
component where concrete is utilized to fill in the steel
tubes. At this present day it is broadly known that
application of more than two materials in a structure
specially can give raise to an efficient system in order to
resist seismic forces. Use of such composite structural
member has been tremendously increased all over the world
during these past few years.
Composite column members are very important application
in the field of composite constructions. Application of
composite column members can result in savings of
dimension of column, which leads to the economic savings
in structure construction. The minimization in column
dimension provides substantial benefits such as larger floor
area like in car parks and office blocks. Also in slender
column members, where severe buckling will occur, the
steel tube will provide significantly to the strength. The steel
casing confines the concrete core and filled concrete inhibits
local buckling of the steel tubes which is the main reason for
the member to carry maximum load.
CFST members are basically suited for varieties of
applications because of their effective using of construction
material. These composite elements are capable of carrying
large amount of axial load and widely used because of its
high stiffness, high ductility, large capacity of energy
absorption and high strength.
Circular steel tube sections poses a benefit compared to
different sections when they are used as compression
member. Consider a particular cross sectional, they have a
large uniform elastic stiffness about every direction and by
filling the empty steel tubes with concrete build an effective
definitive strength of the part with vey less noteworthy
increment of expense. The main reason of filling concrete in
steel tubes is because it can postpone the local buckling of
outer casing of CFST i.e., steel tube and concrete core will
also be in a controlled manner, and it has the capacity to
withstand greater stresses and strains than when the segment
is uncontrolled.
2. METHODOLOGY
The following specimens are tested using compressive
testing machine of 2000KN capacity in order to determine
buckling load, rupture load and deformation for a same
section specimens by varying the stiffeners and stiffeners
providing height. The specimens given below are for testing
at 7days, 28days and 56 days respectively as given below.
The steel tubes sections were cut from the original 6m steel
tube and the ends were mounded according to dimensions
using cutting machine. The inside of the steel tubes are
brushed using metal wires to remove any rust and loose
debris. The deposits such as any grease and oil were
removed away too. One end of the tube was sealed by plates
in order to prevent any seepage during concrete pouring, and
then the tubes were placed upright with the sealed end on a
leveled white board to ensure stability during concrete
pouring.

2. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 05 Issue: 08 | Aug-2016, Available @ http://ijret.esatjournals.org 69
Total 36 specimens were casted by filling self-compacting
concrete in prepared steel tubes. The concrete filled kept
away from any vibration to ensure self-compacting.
The models were placed upright to air-dry, and all loose
mortar was removed from the top surface of the hardened
concrete after 1 day, then the curing of CFST was done by
covering the specimen with gunny bags, after wetting the
top surface in order to avoid development of cracks and
shrinkage in concrete.
Table 1: Number of specimens casted
Specimens
without
stiffener
single
stiffener
double
stiffeners
7 28 56 7 28 56 7 28 56
days
Hollow steel tubes in no’s 3 3 3
Triple blended SCC filled steel tubes in no’s
3 3 3 3 3 3 3 3 3
3. STIFFENERS
Stiffeners are the structural members used to delay the
buckling of column by increasing its strength. In this
experiment, investigation is done by proving a single
stiffener at mid height (h/2) and providing double stiffeners
at h/3 for the specimens respectively. The stiffeners ends are
fully welded to inner side of the steel tube in the form of
plus symbol as shown below.
Fig-1: Machine cut steel tube and welding of stiffeners
Fig-2: Single stiffened specimen
Fig-3: Double stiffened specimen
4. EXPERIMENTAL PROGRAM
4.1 General
In this work, mild steel tubes are used in preparation of the
specimens which were manufactured in Karnataka, India.
The steel tube sections were cut from the original 6 m steel
tube and the ends machined to meet required length. The
dimension of cross section is of 100mm diameter with
height of 300mm and thickness of 2mm. The Stiffeners are
used to strengthen the hollow steel tube columns and SCC
filled steel tube columns. A total of 27 stub columns under
monotonic compression load were tested in order to
discover the best configuration of the stiffeners for
confining column system (without or with stiffener at h/2 &
h/3 of specimen respectively).
4.2 Dimension of Tube
The dimension of the specimen is taken according to the
limiting value of AISC 360-10.
D/t ≤ 0.31E/Fy.

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4.3 Workability Tests on SCC
Table 2: Workability tests on SCC
Property
Test
method
Unit
Value
obtained
Filling Ability
Slump
Flow
mm 670
Passing
Ability
L-Box H1/H2 0.9
Segregation
Resistance
V-Funnel Seconds 10
4.4 Properties
Table: 3 Properties of steel tube
Sl.no Description symbol value
1 Yield strength Fy 310Mpa
2 Young’s modulus Es 200 Gpa
3 Poisson ratio µ 0.3
4 Density ρ 7800Kg/m3
5 Diameter D 300mm
6 Height h 100mm
7 Thickness t 2mm
Concrete type = Triple blended SCC.
Pozzolonic material = Cement, Fly ash, GGBS.
Percentage of pozzolonic material:
Cement=40%, Fly ash=30%, GGBS=30%.
Aggregates size = 12.5mm down size.
Grade of concrete = M50.
Proportion = 1: 1.72: 1.6: 0.38
(cementitious: Fine aggregate: Course aggregate: w/c)
Plasticize = Glenium- B233 (0.3%).
Stiffeners height:
Single stiffener = h/2 & Double stiffeners=h/3.
Fig-4: Casted specimens
5. RESULTS
After casting the composite concrete filled steel tubes they
are cured and tested for 7days, 28days and 56 days using
CTM of 2000KN capacity under loading rate of 40KN per
minute. The deformation values through dial gauge are
noted down at every 5KN interval until the specimen fails to
carry the load. The load carrying capacity of unstiffened,
single stiffened and double stiffened is shown in below
tables
Fig-5: Testing of specimen using CTM & Specimen after
failure
Table 4: ultimate load carrying capacity
Description
Average
Ultimate
load in
KN
Theoretical Ultimate load in
KN
ACI
British
Standa
rd 5400
Europe
an
Code
EC4
7
28
56
7
28
56
7
28
56
7
28
56
days
Hallow
zero
stiffened
158 154 154 154
Hallow
single
stiffened
200 154 154 154
Hallow
double
stiffened
210 154 154 154
CFST
zero
stiffened
451
594
670
364
510
574
319
435
485
401
573
648
CFST
single
stiffened
473
610
710
CFST
double
stiffened
496
660
763

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Volume: 05 Issue: 08 | Aug-2016, Available @ http://ijret.esatjournals.org 71
Fig-6: Comparison of Load v/s deformation curve b/w HST
and CFST for 7-days strength
Fig-7: Comparison of Load v/s deformation curve b/w HST
and CFST for 28-days strength
Fig-8: Comparison b/w HST and CFST for 56-days strength
Fig-9: Comparison of ultimate load b/w experimental &
theoretical values for 7-days strength
Fig-10: Comparison of ultimate load b/w experimental &
theoretical values for 28-days strength
Fig-11: Comparison of ultimate load b/w experimental &
theoretical values for 56-days strength
0
100
200
300
400
500
600
700
0 1 2 3 4
LoadinKN
Deformation in mm
Load v/s Deformation for7-days strength of
CFST
hollow zero
stiffener
hallow single
stiffened
hallow double
stiffened
zero stiffened
CFST
single stiffened
CFST
double stiffened
CFST
0
100
200
300
400
500
600
700
0 2 4 6 8
LoadinKN
Deformation in mm
Load v/s deformation for 28days strength of CFST
hollow zero
stiffened
hallow single
stiffened
hallow double
stiffened
0
100
200
300
400
500
600
700
800
0 2 4 6
LoadinKN
Deformation in mm
Load v/s deformation for 56days strength of CFST
hollow zero
stiffened
hallow
single
stiffened
hallow
double
stiffened
zero
stiffened
CFST
0
50
100
150
200
250
300
350
400
450
500
zero
stiffened
single
stiffened
double
stiffened
LoadinKN
Number ofstiffeners
Comparison of 7-days ultimate load
hallow steel tubes
CFST
ACI-1999
BS 5400
EC 4
0
100
200
300
400
500
600
700
zero
stiffened
single
stiffened
double
stiffened
LoadinKN
Number ofstiffeners
Comparision of 28-days ultimate load
hallow steel tubes
CFST
ACI-1999
BS 5400
EC 4
0
100
200
300
400
500
600
700
800
zero
stiffened
single
stiffened
double
stiffened
LoadinKN
Number ofstiffeners
Comparision of 56-days ultimate load
hallow steel tubes
CFST
ACI-1999
BS 5400
EC 4

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Volume: 05 Issue: 08 | Aug-2016, Available @ http://ijret.esatjournals.org 72
6. CONCLUSION
1. Use of triple blended SCC as a filling component in
steel tubes made the composite element to carry greater
axial load compared to hollow steel tubes.
2. The workability of SCC is better because of increase in
finer particles by use of triple blending (Cement, Fly
ash, GGBS).
3. The load carrying capacity of stiffened specimens is
more compared to unstiffened specimens.
4. The combination of double stiffeners at a height of h/3
from the ends of CFST provided maximum load
carrying capacity compared to single stiffened
specimens and zero stiffened specimens.
5. Ultimate load of single stiffened CFST is more than that
of the ultimate of zero stiffened CFST specimens.
6. The load carrying capacity increases as the strength of
triple blended SCC increases.
7. Experimental ultimate load of CFST stiffened element
is more compared to theoretical ultimate load from BS
4500, EC 4 and ACI code.
ACKNOWLEDGEMENTS
I am thankful to Mrs.Sharada S A and Dr.G Narayana for
their guidance. I also thank department of civil engineering
S J C institute of technology, chickallapura. And last but not
the least my parents who have supported me to complete
this project work.
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BIOGRAPHY
NAVEEN KUMAR Y R Obtained B.E
degree in Civil Engineering (First class
with distinction) during the year 2014
from S J C Institute of Engineering
chickballapur Affiliated to VTU Belgaum.
Presently perusing Master of Technology
in Structural Engineering at S J C Institute
of Engineering